Channel shapes split microdrops

March 10/17, 2004

One important component of labs-on-a-chip
is the capability of handling tiny volumes of liquid precisely. Researchers
from Harvard University have come up with a method for breaking larger
drops into daughter drops of specific volumes.

The method is passive; it uses the pressure-driven flow of liquid
through microscale channels containing T-shaped junctions or isolated
obstacles to create the daughter drops.

The method could be used in future labs-on-a-chip to, for example,
break off a portion of a reaction that is taking place in a droplet in
order to analyze the reaction at that point.

The researchers used a 30-micron-wide channel that led to a T-junction.
Under pressure each droplet is halved at the intersection. The researchers
were able to create unevenly split droplets by changing the shape of the
T. When they made the arms different lengths, the shorter arm had faster
flowing fluid and ended up with a larger fraction of each water droplet.

The researchers also used a series T-junctions to break up a droplet
into a sequence of smaller droplets. The researchers also showed that
it was possible to break up droplets by putting a square obstacle either
in the center or on one side of a channel.

The method could be used in practical applications in two to five
years, according to the researchers. The work is slated to appear in an
upcoming issue of Physical Review Letters.